A Formal Nitrogen Atom Insertion into N‐Aroyl‐7‐Azaindoles Toward Blocked Isocyanates for the Synthesis of Unsymmetrical Ureas

The interaction of TMSN 3 with N ‐aroyl‐7‐azaindoles in the presence of an acid catalyst resulted in a formal nitrogen atom insertion, leading to the synthesis of N ‐phenyl‐1H‐pyrrolo[2,3‐b]pyridine‐1‐carboxamides, a novel class of blocked isocyanates. Mechanistic investigations demonstrated that the key step in the reaction was the Curtius rearrangement, which involves a sequence of elimination and addition processes of the 7‐azaindole moiety. Furthermore, transamidation of these carboxamides with various amines was successfully conducted to produce unsymmetrical ureas.